Refrigeration and air conditioning hose is employed to transfer refrigerant between the various refrigeration circuit components. With smaller sizes of refrigeration circuits, such as used with residential and automobile air conditioning systems relatively small diameter flexible refrigerant hose may be used wherein the hose includes an inner tube formed of a thermoplastic material, such as nylon, which minimizes permeation of the refrigerant gas. However, because thermoplastic inner tubes of larger diameter, such as above 3/4 inch ID, are relatively stiff and do not readily deform or bend, nylon refrigerant hose inner tubes are not commonly employed with such larger diameter refrigerant hose as used in industrial applications, and with air conditioning systems for buses and trucks. Accordingly, with higher capacity refrigeration circuits pre-formed metal conduit is usually employed, necessitating higher costs and requiring skilled installation as compared to circuits employing flexible conduit of smaller size. If larger flexible diameter refrigeration hose assemblies are required rubber is normally employed as the hose inner tube material to provide the desired flexibility, but rubber is permeated by refrigerant gases and the gases will slowly escape to the atmosphere creating an undesirable environmental hazard and require frequent circuit recharging. Presently, refrigerant hose of larger diameter having a highly flexible inner tube formed of a low refrigerant permeability material is not available for refrigeration circuits.
It is known to improve the flexibility characteristics of flexible hose by using a corrugated inner tube construction, such as shown in the assignee's U.S. Pat. No. 4,758,029. Hose having an inner tube formed of corrugations is capable of excellent lateral flexibility without kinking or collapse. However, in order to achieve the desired resistance to internal pressures, abrasion, and the like corrugated hose inner tubes are usually surrounded by protective covers or braided pressure resistant layers which are bonded to each other by vulcanizing, adhesives, or the like. The bonding of adjacent hose layers detracts from the lateral flexibility of the hose as relative axial displacement between adjacent hose layers is not permitted and the advantages achieved by the inner corrugated tube are, to some extent, negated.
While it has been appreciated that thermoplastics, such as nylon, have low permeability when conveying refrigeration gases, such materials when used as a refrigeration conduit inner tube have the disadvantage of being adversely affected by moisture from the atmosphere, and this characteristic of nylon has detracted from its use in refrigeration circuits in that refrigeration circuits are particularly susceptible to moisture contamination.